This invention relates generally to controlling the orientation of assemblies, such as valves and associated components, of the type suspended in a borehole. More particularly, it relates to a method and apparatus for insuring that a communication sensor or other component of an assembly suspended within a borehole, such as a gas or oil production well, retains a fixed angular orientation relative to such borehole.
It is often desirable to provide in a production gas or oil well, a component of some sort down the borehole adjacent, for example, an oil bearing strata from which a desired product is being produced. This component may simply be a safety valve or the like to selectably stop the flow of crude oil through the production tubing. It also may be monitoring instrumentation, some of which is relatively sophisticated, which gathers desired information relating to the borehole or the product. In any event, it is necessary to communicate with such apparatus from the surface.
Various mechanisms for providing downhole communication have been designed and used. The reliability of these mechanisms, though, generally is a function of the depth of the communication. That is, the reliability of a communication between a downhole apparatus and the location on a surface between which a communication is desired, is dependent upon the distance between such locations. Thus, deep communication has not in the past been as reliable as desired. Many of such mechanisms have used hydraulic communication via flowing product. A difficulty with this type of mechanism is that typically there must be well casing penetration or other fluid accessability at the well head in order to provide physical access for such communication. Thus, the well head is exposed to blow-out. An electric control line is sometimes provided, extending from the surface to the downhole apparatus. There are additional problems associated with control of this type. For example, the installation of wire linkage can be difficult--for example, it is typical that the linkage be installed with the individual string sections making up the production tubing as they are lowered into the borehole. Breakage often occurs either during such installation or later.
It is known that it is desirable to provide wireless communication, e.g., communication via an electromagnetic link, with the downhole location. The reliability of wireless communication is limited, however, when the electrical component of an electromagnetic wave is detected to obtain the desired information. The earth, the medium through which essentially all of such communication takes place, includes many anomalies responsible for interference with such an electrical component of an information signal. Moreover, the metallic casing used to line boreholes effectively shields an electric sensor from such a component.
One way of avoiding the problems of the detection of the electrical component of an electromagnetic wave for communications purposes, is to detect the magnetic component of such a wave. U.S. Pat. No. 3,967,201 naming Louis H. Rorden, an inventor hereof, as the inventor is directed to such a communication scheme. This communication typically is achieved utilizing a magnetic sensor at the downhole location.
It is important in achieving reliable communication that stray noise and interference which can be picked up by the downhole sensor be minimized. The magnetic components of electromagnetic signals used for communication typically are at relatively low frequencies, e.g., below 1 kilohertz. Communication at low frequencies is especially prone to noise interference since low frequency noise is more easily induced or otherwise present in downhole environments. For example, at low frequencies mechanical vibrations of the production tubing and even of the earth can result in interference.
The generation of stray noise is particularly a problem in downhole communications since the sensor often is a component of a safety valve or other assembly suspended from a tailpipe section of production tubing, which in turn, is typically suspended below a packer in the fluid being produced. Vibration easily can be induced in such suspended members. Such vibration can create noise which will interfere with the reliable operation of the communication link.